expression, godan verb (-u)
have an accident; meet with an accident
Standard phrase for being involved in an accident, typically a traffic or work-related accident. The verb あう (遭う) implies encountering something undesirable.
昨日、友達が事故にあって入院した。
Yesterday my friend had an accident and was hospitalized.
交通事故
Please be careful not to get into a traffic accident.